Conservation of the pure adiabatic state in Ehrenfest dynamics of the photoisomerization of molecules

Abstract

We examined real-time-propagation time-dependent density functional theory (rtp-TDDFT) coupled with molecular dynamics (MD), which uses single-particle representation of time-evolving wavefunctions allowing exchange of orbital characteristics between occupied and empty states making the effective Kohn-Sham Hamiltonian dependent on the potential energy surfaces (PESs). This scheme is expected to lead to mean-field average of adiabatic potential energy surfaces (PESs), and is one of Ehrenfest (mean-field) approaches. However, we demonstrate that the mean-field average can be absent in simulating photoisomerization of azobenzene and ethylene molecules. A transition from the S2 to the S1 excited state without the mean- field average was observed after examining several rtp-TDDFT-MD trajectories of a photoexcited azobenzene molecule. The subsequent trans-cis isomerization was observed in our simulation, which is consistent with experimental observation and supported by previous calculations. The absence of the mean-field average of PESs was also observed for the transition between the S1 and S0 states, indicating that the MD simulation was on a single PES. Conversely, we found no transition to the ground state (S0 state) when we performed a MD simulation of an S1 excited ethylene molecule owing to the constraint on the occupation number of each molecular orbital. Thus, we conclude that, at least for azobenzene and ethylene molecules, the rtp-TDDFT-MD is an on-the-fly simulation that can automatically see the transition among the PESs of excited states without the mean-field average unless the simulation reaches the PES of the S0 state.

Molecular-scale modeling of light emission by combustion: An ab initio study

“…For an incident kinetic energy of 6 eV, the time evolution of the potential energy obtained by TDDFT was finally located slightly above the PES of the ground state, but this was far below the lowest excited PESs obtained by the ΔSCF calculation. This result may correspond to the PES mixing discussed in previous works 26,27 . As shown in the insets in the bottom of Fig.…”

Proton-transfer dynamics in ionized water chains using real-time time-dependent density functional theory

“…As shown in electronic forces governing the motion of the proton. In principle, a comparison of the initial behavior of adiabatic and nonadiabatic dynamics highlights the mean-field averaging effect of the PESs inherent in the Ehrenfest approach [23,[58][59][60].…”

“…A principal aim of our work is to develop physical intuition for a more tractable system comprising of water molecules and examine proton-transfer probability [P(PT)] as computed by real-time time-dependent density functional theory (rt-TDDFT)-based [19,20] Ehrenfest dynamics [21][22][23][24] upon "photoionization" of such systems. The main idea behind this study is to identify a practical and reliable method to study more complex systems.…”

Modeling of laser-pulse induced water decomposition on two-dimensional materials by simulations based on time-dependent density functional theory

“…(The current Ehrenfest MD approach in such a long-time simulation will be validated by using the method in Ref. [20]).…”

“…The validity of this approach has been discussed in Refs. [19,20], in which the results without strong nonadiabatic coupling were expected to work properly. We solved the time-dependent Kohn-Sham equation…”